The invention relates to a cleaning sub system in an imaging system and more particularly to a cleaning mechanism for removing residual toner and debris from a charge retentive surface including a secondary cleaning system for release and removal of agglomerations that are not cleaned therefrom at the primary cleaner.
In electrostatographic printing such as electrophotography, image transfer from the charge retentive surface to the printing substrate (such as paper) is known to at times be incomplete. In response, primary cleaning systems were developed to remove residual toner from the charge retentive surface prior to the next image development procedure. Such primary cleaning systems include one or more rotating electrostatic brushes, cleaning blades, electrostatic air cleaners, vacuum systems, and other similar systems used singly or in combination. For over a decade, the art of electrostatographic printing has understood that certain agglomerations of toner particles and other materials can stick to photoreceptors or other charge retentive surfaces sufficiently to resist removal by primary cleaning systems. Such agglomerations have multiple causes, including melting of toner resins, adherence of random glue materials transferred from printing substrates, paper fibers and other debris, and a combination of mechanical and electrostatic forces. Residual agglomerations can cause imaging defects such as streaks and spots. The longer the agglomerations are allowed to remain on the charge retentive surface, the harder they often become to remove. Additional material tends to build in the lee of initial agglomeration spots, and the combination of initial agglomerations and added material often forms agglomerations shaped like and sometimes named “comets”.
In response, secondary cleaning systems were installed. As taught in U.S. Pat. No. 4,989,047 issued to Jugle et al. and U.S. Pat. No. 5,031,000 issued to Pozniakas, et al., such a secondary cleaning system can comprise a relatively hard cleaning “spot” blade located downstream from the primary cleaning system for the purpose of shearing agglomerations that resist initial cleaning away from the imaging surface. Various improvements to this secondary cleaning system have been introduced, including improved design of the blade to resist blade tucking (See, U.S. Pat. No. 5,349,428 issued to Derrick) and improved blade materials (See, e.g., U.S. Pat. No. 5,339,149 issued to Lindblad; U.S. Pat. No. 5,732,320 issued to Domagall et al.; and U.S. Pat. No. 6,282,401 issued to Proulx et al.) In particular, Lindblad is significant since it recognizes that friction between the blade and the charge retentive surface causes heat that in turn causes certain agglomerations to adhere even more tightly to the surface and further resist cleaning. Each of these references cited above are hereby incorporated herein in their entirety.
Even with the improvements referenced above, present techniques fail to completely remove harmful agglomerations. In particular, agglomerations that are lifted from the charge retentive surface sometimes stick to the spot blade itself rather than falling away or being removed by vacuum pressure. As the spot blade continues to press lightly against the photoreceptor or other charge retentive surfaces, stuck agglomerations slowly begin to mar the surface layers of the photoreceptor. Eventually, these micro-scratches wear enough from the photoreceptor that the scratches become visible in the developed images as streaks. At such time, good practice is to replace the photoreceptor. Often, the actual or expected appearance of such streaks sets the recommended time for replacement of the photoreceptor, even though, without such streaks, the photoreceptor remain within acceptable specifications for a considerably longer service life.
It would be desirable to have a spot removing system that successfully removes spots and that ameliorates the tendency for agglomerations on the spot blade to mar the surface of a photoreceptor or other charge retentive device. Such an improved spot removing system would decrease the cost of ownership of printing systems containing such system by extending the service life of a typical photoreceptor or other imaging surface. Additionally, image quality will be enhanced by ameliorating micro-scratches caused by such agglomerations.
One aspect of the invention is a cleaning system for removing residual toner from an imaging surface, comprising: a primary cleaner for removing the predominant amount of residual toner and debris, such primary cleaner having an operative position; a blade holder; an agglomeration cleaning blade mounted in the blade holder at a position downstream from the primary cleaner, said cleaning blade having a cleaning edge; and a forcing device for moving the blade between a first and a second position wherein the first and second position are selected from the group consisting of an engaged position and a retracted position; wherein, when the blade is moved into the engaged position, the cleaning edge is supported at a low angle of attack in engagement with the imaging surface at a relatively low load, for shearing release of agglomerations from the imaging surface and wherein the cleaning blade is movable to the retracted position during periods in which the primary cleaner is in its operative position.
Another aspect of the invention is a process for cleaning agglomerations from an imaging surface, comprising: removing the predominate amount of residual toner and debris from the imaging surface by a primary cleaner mechanism; engaging a cleaning edge of a cleaning blade with the imaging surface at a low angle of attack at a relatively low load for shearing release of agglomerations from the imaging surface; retracting the cleaning blade from the position in which it is engaged with the imaging surface; and cleaning the retracting cleaning blade by engaging the cleaning edge with a wiper mechanism.